This invention relates to bisimide compositions and more particularly to such compositions modified for flame-retardancy, and to a process for producing same.
Bisimide compositions containing unsaturated reactive groups are known as components of thermoset resins useful as adhesives in laminates for the electronics industry such as printed wiring boards, thermoset molding components, honeycomb structures and the like. Typically the bisimide composition is chain extended or partially polymerized, usually with one or more coreactants, to form a prepolymer, then applied to components of the laminate and cured at elevated temperature and pressure, sometimes with additional coreactants and usually in the presence of a crosslinking agent. The resulting thermoset structure resists deterioration at high use temperatures on the order of about 250.degree.-300.degree. C.
Flame-retardance (sometimes herein called "flame resistance") is desirable in commercial applications of these thermoset resins. As used herein, flame retardance means capability of passing Underwriters Laboratories Inc. Standard Test for Flammability of Plastic Materials for Parts in Devices and Appliances, passing Material Classification UL 94V-1, preferably V-0 thereof. In the past flame retardance was achieved by adding halogen compounds to the partially polymerized prepolymer before final elevated temperature curing. See, for example, U.S. Pat. No. 5,004,775, issued Apr. 2, 1991, where octabromodiphenyl oxide is used. Also used were halogen compounds which copolymerize with the bisimide compositions during formation of the prepolymer before curing. See, for example, U.S. Pat. No. 4,876,325, issued Oct. 24, 1989, Example 2 where brominated bisphenol A is used. Unfortunately, during elevated temperature curing, such external flame-retardant additives volatilize to cause blistering and undesirable layer separation of the laminated board and loss of flame resistance.
It would be desirable to improve the flame-retardant performance of such bisimide compositions in these high temperature applications.